Using laser echo recovery and a scannable field-of-view telescope to determine vegetation structure and sub-canopy topography over wide swaths

Building upon several years of aircraft laser altimetry development, a system capable of mapping surface height distributions across wide, nadir-centered swaths has been developed at NASA/Goddard Space Flight Center. The Laser Vegetation Imaging Sensor (LVIS) system can be used to construct maps of precise surface elevations and 3D vegetation canopy structure. The quality of the derived data products as well as satellite-like footprint sizes are maintained using novel laser output and receiver field of view (FOV) scanning techniques. The sensor concept is based on rapidly scanning a laser beam and the telescope FOV across the flight track of the aircraft using small, galvanometer-controlled mirrors. The data products that this system can produce range from simple topographic mapping swaths to 3D vegetation structure mapping. Using the waveform digitizer to capture the return echo from each channel allows us to reconstruct the surface height distribution (SHD) from within each laser footprint. Tree heights, canopy architecture, and surface elevation and roughness beneath canopies can be extracted from the return echo. Adding the 2-color capability allows normalized difference vegetation index (NDVI) measurements through the entire depth of the canopy with 30 cm vertical resolution, thus providing a measure of leaf surface area height distributions. The raster scan pattern of contiguous footprints resulting from positioning the laser beam and telescope FOV across the aircraft flight track covers 100% of the underlying terrain. Statistical analysis of derived SHDs, local surface slopes, and roughness data can thus be performed without making any a priori assumptions about the nature of the slope/height distributions.